III-nitride semiconductor light emitting device

ABSTRACT

The present invention relates to a III-nitride semiconductor light emitting device comprising a plurality of III-nitride semiconductor layers including an active layer emitting light by recombination of electrons and holes, the plurality of III-nitride semiconductor layers having a p-type III-nitride semiconductor layer at the top thereof, a Si a C b N c  (a≧0,b&gt;0,c≧0) layer grown on the p-type III-nitride semiconductor layer, the Si a C b N c  layer having an n-type conductivity and a thickness of 5 Å to 500 Å for the holes to be injected into the p-type III-nitride semiconductor layer by tunneling, and a p-side electrode formed on the Si a C b N c  layer. According to the present invention, a Si a C b N c  (a≧0,b&gt;0,c&gt;0) layer which can be doped with a high concentration is intervened between a p-type nitride semiconductor layer and a p-side electrode. Therefore, the present invention can solve the conventional problem.

TECHNICAL FIELD

The present invention relates to a III-nitride semiconductor lightemitting device, and more particularly, to a III-nitride semiconductorlight emitting device in which contact resistance between a p-typenitride semiconductor layer and a p-side electrode adjacent to thep-type nitride semiconductor layer is reduced and holes are thuseffectively supplied to an active layer. In this case, the III-nitridesemiconductor light emitting device refers to a light emitting devicesuch as a light emitting diode including an Al(x)Ga(y)In(1-x-y)N (0≦x≦1,0≦y≦1, 0≦x+y≦1) compound semiconductor layer, but does not excludesemiconductor layers or materials made of elements of different groups,such as SiC, SiN, SiCN and CN.

BACKGROUND ART

FIG. 1 is a cross-sectional view illustrating the structure of aIII-nitride semiconductor light emitting device in the prior art. Thelight emitting device includes a substrate 100, a buffer layer 200epitaxially grown on the substrate 100, an n-type nitride semiconductorlayer 300 epitaxially grown on the buffer layer 200, an active layer 400epitaxially grown on the n-type nitride semiconductor layer 300, ap-type nitride semiconductor layer 500 epitaxially grown on the activelayer 400, a p-side electrode 600 formed on the p-type nitridesemiconductor layer 500, a aside bonding pad 700 formed on the p-sideelectrode 600, and an n-side electrode 800 formed on an n-type nitridesemiconductor layer 301 which is exposed by mesa-etching at least thep-type nitride semiconductor layer 500 and the active layer 400.

The substrate 100 can use a GaN-based substrate as a homogeneoussubstrate, and a sapphire substrate, a silicon carbide substrate or asilicon substrate as a heterogeneous substrate, but can use any othersubstrates on which nitride semiconductor layers can be grown. If thesilicon carbide substrate is used, the n-side electrode 800 can beformed on the opposite side of the silicon carbide substrate.

The nitride semiconductor layers epitaxially grown on the substrate 100are usually grown by means of MOCVD (Metal Organic Chemical VaporDeposition) method.

The buffer layer 200 serves to reduce differences in lattice constantand the coefficient of thermal expansion between the heterogeneoussubstrate 100 and the nitride semiconductor. U.S. Pat. No. 5,122,845discloses a technology in which an AlN buffer layer having a thicknessof 100 Å to 500 Å is grown on a sapphire substrate at a temperatureranging from 380° C. to 800° C. U.S. Pat. No. 5,290,393 discloses atechnology in which an Al(x)Ga(1-x) N (0≦x<1) buffer layer having athickness of 10 Å to 5000 Å is grown on a sapphire substrate at atemperature ranging from 200° C. to 900° C. Korean Patent No. 10-0448352discloses a technology in which a SiC buffer layer is grown at atemperature ranging from 600° C. to 990° C., and an In(x)Ga(1-x)N(0<x≦1) layer is grown on the SiC buffer layer.

In the n-type nitride semiconductor layer 300, at least a region (n-typecontact layer) in which the n-side electrode 800 is formed is doped withan impurity. The n-type contact layer is preferably made of GaN and isdoped with Si. U.S. Pat. No. 5,733,796 discloses a technology in whichan n-type contact layer is doped with a desired doping concentration bycontrolling a mixing ratio of Si and other source materials.

The active layer 400 is a layer for emitting a photon (light) byrecombination of electrons and holes, and is mainly made ofIn(x)Ga(1-x)N (0<x<1). The active layer 400 is composed of a singlequantum well or multi quantum wells. WO02/021121 discloses a technologyin which only some of a plurality of quantum wells and barrier layersare doped.

The p-type nitride semiconductor layer 500 is doped with an impuritysuch as Mg, and has a p-type conductivity through an activation process.U.S. Pat. No.5,247,533 discloses a technology in which a p-type nitridesemiconductor layer is activated by means of irradiation of electronbeam. U.S. Pat. No.5,306,662 discloses a technology in which a p-typenitride semiconductor layer is activated through annealing at atemperature of 400° C. or more. Korean Patent No.10-0432246 discloses atechnology in which NH3 and a hydrazine-based source material are usedtogether as a nitrogen precursor for growing a p-type nitridesemiconductor layer, so that the p-type nitride semiconductor layer hasa p-type conductivity without an activation process.

The p-side electrode 600 serves to allow the current to be supplied tothe entire p-type nitride semiconductor layer 500. U.S. Pat. No.5,563,422 discloses a technology of a light-transmitting electrode,which is formed almost on the entire p-type nitride semiconductor layer,in ohmic contact with the p-type nitride semiconductor layer, and madeof Ni and Au. Meanwhile, the p-side electrode 600 can be formed to havesuch a thick thickness that the p-side electrode 600 does not transmitlight, i.e., the p-side electrode 600 reflects light toward thesubstrate. A light emitting device using this p-side electrode 600 iscalled a flip chip. U.S. Pat. No.6,194,743 discloses a technology of anelectrode structure including an Ag layer of 20 nm or more in thickness,a diffusion barrier layer covering the Ag layer, and a bonding layermade of Au and Al, which covers the diffusion barrier layer.

In the III-nitride semiconductor light emitting device, the efficiencyof a device can be defined as the ratio of the intensity of lightgenerated to external input power. The p-type GaN constituting thep-type nitride semiconductor layer 500 is not good because it has ahigher energy bandgap (˜3.3 eV) and a doping efficiency of below 5×10¹⁷atoms/cm³. Further, contact resistance between the p-type nitridesemiconductor layer 500 and the p-side electrode 600 adjacent to thep-type nitride semiconductor layer 500 is very high. Accordingly, notonly the efficiency of a device is not good, but also a higher voltageis needed in order to have the same intensity of light.

In order to reduce the contact resistance between the p-type nitridesemiconductor layer 500 and the aside electrode 600, p-type GaN dopedwith a high concentration must be formed. It is, however, very difficultto form p-type GaN doped with a high concentration because of a greatbandgap and a low doping efficiency (<5×10¹⁷atoms/cm³) of the p-typeGaN.

A variety of methods have been proposed in order to reduce the contactresistance between the p-type GaN used as the p-type nitridesemiconductor layer 500 and the p-side electrode 600. Among them, thereis a method in which the p-type nitride semiconductor layer 500 is notmade of a single p-type GaN layer, but is formed to have a superlatticestructure of p-type GaN/p-type InGaN or p-type GaN/p-type AlGaN, and theconcentration of holes, which is significantly higher than theconcentration that can be obtained in the single p-type GaN layer, isthus obtained within the superlattice structure through piezoelectricfield. This method, however, is not preferred because potential barrieris formed in a vertical direction within the superlattice structurebefore holes are injected into the active layer.

As another example, there is a method in which a GaAs layer or an AlGaAslayer is grown, which can be doped with a high concentration (>1020atoms/cm3), between the p-type nitride semiconductor layer 500 and thep-side electrode 600 (U.S. Pat. No.6,410,944). In this method, however,since the bandgap of the GaAs layer or the AlGaAs layer is smaller thanthat of the visible region, most of light generated from the activelayer 400 may be absorbed by the GaAs layer or the AlGaAs layer.Therefore, this method has limited application fields.

As described above, the conventional III-nitride semiconductor lightemitting device is disadvantageous in that the efficiency is low becausethe contact resistance between the p-type nitride semiconductor layer500 and the p-side electrode 600 is high. In this connection, there is aneed for effective means for overcoming this problem.

DISCLOSURE

Technical Problem

Accordingly, the present invention has been made in view of the aboveproblems occurring in the prior art, and it is an object of the presentinvention to provide a II-nitride semiconductor light emitting devicehaving improved efficiency, in which contact resistance between a p-typenitride semiconductor layer and a p-side electrode formed on the p-typenitride semiconductor layer is reduced.

Technical Solution

To achieve the above object, according to the present invention, thereis provided a III-nitride semiconductor light emitting device, includinga plurality of III-nitride semiconductor layers including an activelayer emitting light by recombination of electrons and holes, theplurality of III-nitride semiconductor layers having a p-typeIII-nitride semiconductor layer at the top thereof, an Si_(a)C_(b)N_(c)(a≧0,b>0,c≧0,a+c>0) layer grown on the p-type III-nitride semiconductorlayer, the Si_(a)C_(b)N_(c) (a≧0,b>0,c≧0,a+c>0) layer having an n-typeconductivity and a thickness of 5 Å to 500 Å for the holes to beinjected into the p-type III-nitride semiconductor layer by tunneling,and a p-side electrode formed on the Si_(a)C_(b)N_(c)(a≧0,b>0,c≧0,a+c>0) layer.

In the present invention, the thickness of the Si_(a)C_(b)N_(c)(a≧0,b>0,c≧0,a+c>0) layer has a restriction, so that tunneling isefficiently accomplished. Also, when the Si_(a)C_(b)N_(c)(a≧0,b>0,c≧0,a+c>0) layer is made of SiC, the degradation of theplurality of III-nitride semiconductor layers caused by decomposition ofnitrogen therefrom during the growth of SiC layer is considered in thisrestriction.

In addition, according to the present invention, there is provided aIII-nitride semiconductor light emitting device, including a pluralityof III-nitride semiconductor layers including an active layer emittinglight by recombination of electrons and holes, the plurality ofIII-nitride semiconductor layers having a p-type III-nitridesemiconductor layer at the top thereof, a Si_(a)C_(b)N_(c) (a≧0,b>0,c>0)layer grown on the p-type III-nitride semiconductor layer, and a p-sideelectrode formed on the Si_(a)C_(b)N_(c) (a≧0,b>0,c>0) layer.

In the present invention, during the growth of the Si_(a)C_(b)N_(c)(a≧0,b>0,c>0) layer, nitrogen is continuously supplied because theSi_(a)C_(b)N_(c) (a≧0,b>0,c>0) layer includes nitrogen. Thus, thepresent invention has an additional advantage that the decomposition ofnitrogen is prevented by the Si_(a)C_(b)N_(c) (a≧0,b>0,c>0) layer.

In the present invention, the p-side electrode may be made of nickel andgold. The alloy of nickel and gold is the representative materials usedfor the p-side light-transmitting electrode of III-nitride semiconductorlight emitting device.

In the present invention, the p-side electrode may be made of ITO(Indium Tin Oxide). Recently, ITO (Indium Tin Oxide) is widely used as ap-side electrode, but it is not easy to make a good ohmic contact withthe p-type semiconductor using ITO (Indium Tin Oxide). The problem canbe solved by using the Si_(a)C_(b)N_(c) (a≧0,b>0,c≧0,a+c>0) layer with ahigh doping concentration.

Advantageous Effects

Generally, in III-nitride semiconductor light emitting devices, if ap-side electrode is formed directly on a p-type nitride semiconductor,high contact resistance is generated due to a high energy bandgap andlow doping efficiency of the p-type nitride semiconductor. This makesthe efficiency of the device degraded. According to the presentinvention, however, a Si_(a)C_(b)N_(c) (a≧0,b>0,c≧0,a+c>0) layer whichcan be doped with a high concentration is intervened between a p-typenitride semiconductor and a p-side electrode. Therefore, the presentinvention can solve the conventional problem.

DESCRIPTION OF DRAWINGS

Further objects and advantages of the invention can be more fullyunderstood from the following detailed description taken in conjunctionwith the accompanying drawings in which:

FIG. 1 is a cross-sectional view illustrating the structure of aIII-nitride semiconductor light emitting device in the prior art;

FIG. 2 is a cross-sectional view illustrating the structure of aIII-nitride semiconductor light emitting device according to anembodiment of the present invention;

FIG. 3 is a graph showing X-ray diffraction (XRD) analysis of siliconcarbide grown on a sapphire substrate;

FIG. 4 shows an energy band diagram of a metal/n-type SiC/p-type GaNstructure; and

FIG. 5 shows an energy band diagram for explaining the operationalprinciple of the metal/p-type SiC/p-type GaN structure.

MODE FOR INVENTION

The present invention will now be described in detail in connection withpreferred embodiments with reference to the accompanying drawings.

FIG. 2 is a cross-sectional view illustrating the structure of aIII-nitride semiconductor light emitting device according to anembodiment of the present invention.

A buffer layer 11, an n-type nitride semiconductor layer 12, an activelayer 13, and a p-type nitride semiconductor layer 14 are sequentiallygrown on a substrate 10. A p-side electrode 15 and a p-side bonding pad17 are formed over the p-type nitride semiconductor layer 14. An n-sideelectrode 16 is formed on the n-type nitride semiconductor layer 121,which is exposed by mesa etching.

Referring to FIG. 2, unlike the prior art, according to the presentinvention, an n-type or p-type Si_(a)C_(b)N_(c) (a≧0,b>0,c≧0,a+c>0)layer 21 is intervened between the p-type nitride semiconductor layer 14and the p-side electrode 15.

Si_(a)C_(b)N_(c) (a≧0,b>0,c≧0,a+c>0) includes silicon carbide[Si_(a)C_(b)N_(c) (a>0,b>0,c=0)], silicon carbon nitride[Si_(a)C_(b)N_(c) (a>0,b>0,c>0)]0 or carbon nitride [Si_(a)C_(b)N_(c)(a=0,b>0,c>0)], which are a group of materials having the similarproperties.

In the Si_(a)C_(b)N_(c) (a≧0,b>0,c≧0,a+c>0) layer 21, an n-type dopantsuch as Si, N, As or P and a p-type dopant such as B or Al can be easilydoped at a high concentration of about 1×10¹⁸ to 1×10²² atoms/cm³. Thus,the thickness of a potential barrier can be made thin so that holes caneasily pass through the Si_(a)C_(b)N_(c) (a≧0,b>0,c≧0,a+c>0) layer 21.

In FIG. 2, silicon carbide [Si_(a)C_(b)N_(c) (a>0,b>0,c=0)] is used asthe Si_(a)C_(b)N_(c) (a≧0,b>0,c≧0,a+c>0) layer 21. The silicon carbidelayer 21 can be obtained by allowing silicon and carbon to react to eachother in a deposition apparatus. The silicon source material can includeSiH₄, Si₂H₆, DTBSi, etc., and the carbon source material can includeCBr₄, C_(x)H_(y), etc.

Generally, the growth temperature of silicon carbide is over 1300° C. Ifsilicon carbide is formed on a nitride semiconductor such as GaN at toohigh temperature, however, a GaN based device may be damaged whensilicon carbide is grown. Therefore, the growth temperature of siliconcarbide is preferably 600° C. to 1200° C.

Further, if the thickness of the silicon carbide layer becomes toothick, a tunneling barrier undesirably thickens. It is thus preferredthat the thickness of the silicon carbide layer is about 5 Å to 500 Å.The doping concentration, thickness, and the growth temperature of thesilicon carbide layer can be applied to formation of the silicon carbonnitride [Si_(a)C_(b)N_(c) (a>0,b>0,c>0)] layer or the carbon nitride[Si_(a)C_(b)N_(c) (a=0,b>0,c>0)] layer in the same manner as well asformation of the silicon carbide layer. In this case, NH₃ and/orhydrazine-based source can be mainly used as a nitrogen source material.

The p-side electrode 15 and the n-side electrode 16 can be made of atleast one selected from the group consisting of nickel, gold, silver,chromium, titanium, platinum, palladium, rhodium, iridium, aluminum,tin, ITO (Indium Tin Oxide), indium, tantalum, copper, cobalt, iron,ruthenium, zirconium, tungsten, lanthanum and molybdenum.

FIG. 3 is a graph showing X-ray diffraction (XRD) analysis of siliconcarbide grown on a sapphire substrate. In this case, the growthtemperature was 1000° C. and the growth rate was 2 Å/sec. Further, thethickness of grown silicon carbide was 5000 Å for XRD analysis. NH₃ wasused as a N source for high concentration n-type doping. At this time,the doping concentration was 4.63×10¹⁹ atoms/cm³ so that tunneling canoccur sufficiently. From FIG. 3, it can be seen that silicon carbide iswell grown.

Table 1 shows electrical characteristics of a device, which is formed bygrowing silicon carbide of about 20 Å in thickness, which is doped witha high concentration, on a common GaN-based light emitting device. Atthis time, an electrode used was an ITO(Indium Tin Oxide) electrode.From Table 1, it can be seen that a case where a silicon carbide layeris formed has a low contact resistance value compared to a case where anelectrode is formed on p-type GaN without silicon carbide layer.

TABLE 1 CONTACT LAYER Vf@20 mA[V] Vf@10 μA[V] Vr@-10 μA[V] case 1 p-GaN5.25 2.37 24.1 case 2 SiC/p-GaN 3.65 2.35 25.1

FIG. 4 shows a schematic energy band diagram when the n-type siliconcarbide layer 21 exits between the p-type nitride semiconductor layer 14and the p-side electrode 15. From FIG. 4, it can be seen that holes canflow into the p-type nitride semiconductor layer 14 in a more efficientmanner since the n-type silicon carbide layer 21 doped with a highconcentration exists (E_(C): Conduction Band Energy, E_(V): Valence BandEnergy, E_(F): Fermi Energy Level).

FIG. 5 shows a schematic energy band diagram in the case (a) where thep-side electrode 15 is formed on the p-type nitride semiconductor layer14 and the case (b) where a p-type silicon carbide layer doped with ahigh concentration exists between the p-type nitride semiconductor layer14 and the p-side electrode 15. From FIG. 5, it can be seen that holes Hcan flow into the p-type nitride semiconductor layer 14 in a moreefficient manner in the case where there exists the p-type siliconcarbide layer doped with the high concentration (E_(C): Conduction BandEnergy, E_(V): Valence Band Energy, E_(F): Fermi Energy Level).

While the present invention has been described with reference to theparticular illustrative embodiments, it is not to be restricted by theembodiments but only by the appended claims. It is to be appreciatedthat those skilled in the art can change or modify the embodimentswithout departing from the scope and spirit of the present invention.

1. A III-nitride semiconductor light emitting device comprising: aplurality of III-nitride semiconductor layers including an active layeremitting light by recombination of electrons and holes, the plurality ofIII-nitride semiconductor layers having a p-type III-nitridesemiconductor layer at the top thereof, a Si_(a)C_(b)N_(c) (a≧0,b>0,c>0)layer grown on the p-type III-nitride semiconductor layer, wherein theSi_(a)C_(b)N_(c) (a≧0,b>0,c>0) layer has an n-type conductivity and athickness of 5 Å to 500 Å for the holes to be injected into the p-typeIII-nitride semiconductor layer by tunneling, and a p-side electrodeformed on the Si_(a)C_(b)N_(c) (a≧0,b>0,c>0) layer.
 2. The III-nitridesemiconductor light emitting device of claim 1, wherein growthtemperature of a Si_(a)C_(b)N_(c) (a≧0,b>0,c>0) layer is in a range from600° C. to 1200° C.
 3. The III-nitride semiconductor light emittingdevice of claim 1, wherein the doping concentration of theSi_(a)C_(b)N_(c) (a≧0,b>0,c>0) layer is in a range from 1×10¹⁸ to 1×10²²atoms/cm³.
 4. The III-nitride semiconductor light emitting device ofclaim 1, wherein the p-side electrode is made of nickel and gold.
 5. TheIII-nitride semiconductor light emitting device of claim 1, wherein thep-side electrode is made of ITO(Indium Tin Oxide).
 6. The III-nitridesemiconductor light emitting device of claim 1, wherein the p-sideelectrode is made of at least one selected from the group consisting ofnickel, gold, silver, chromium, titanium, platinum, palladium, rhodium,iridium, aluminum, tin, ITO(Indium Tin Oxide), indium, tantalum, copper,cobalt, iron, ruthenium, zirconium, tungsten, lanthanum and molybdenum.